Cholesterol-Independent Effects of Methyl-b- Cyclodextrin on Chemical Synapses

The cholesterol chelating agent, methyl-b-cyclodextrin (MbCD), alters synaptic function in many systems. At crayfish neuromuscular junctions, MbCD is reported to reduce excitatory junctional potentials (EJPs) by impairing impulse propagation to synaptic terminals, and to have no postsynaptic effects. We examined the degree to which physiological effects of MbCD correlate with its ability to reduce cholesterol, and used thermal acclimatization as an alternative method to modify cholesterol levels. MbCD impaired impulse propagation and decreased EJP amplitude by 40% (P,0.05) in preparations from crayfish acclimatized to 14uC but not from those acclimatized to 21uC. The reduction in EJP amplitude in the cold-acclimatized group was associated with a 49% reduction in quantal content (P,0.05). MbCD had no effect on input resistance in muscle fibers but decreased sensitivity to the neurotransmitter L-glutamate in both warm- and coldacclimatized groups. This effect was less pronounced and reversible in the warm-acclimatized group (90% reduction in cold, P,0.05; 50% reduction in warm, P,0.05). MbCD reduced cholesterol in isolated nerve and muscle from cold- and warmacclimatized groups by comparable amounts (nerve: 29% cold, 25% warm; muscle: 20% cold, 18% warm; P,0.05). This effect was reversed by cholesterol loading, but only in the warm-acclimatized group. Thus, effects of MbCD on glutamatesensitivity correlated with its ability to reduce cholesterol, but effects on impulse propagation and resulting EJP amplitude did not. Our results indicate that MbCD can affect both presynaptic and postsynaptic properties, and that some effects of MbCD are unrelated to cholesterol chelation.

Bird depredation of grapes in Niagara vineyards : a novel approach to identifying spatial and temporal trends /

Although local grape growers view bird depredation as a significant economic issue, the most recent research on the problem in the Niagara Peninsula is three decades old. Peer-reviewed publications on the subject are rare, and researchers have struggled to develop bird-damage assessment techniques useful for facilitating management programmes. I used a variation of Stevenson and Virgo's (1971) visual estimation procedure to quantify spatial and temporal trends in bird damage to grapes within single vineyard plots at two locations near St. Catharines, Ontario. I present a novel approach to managing the rank-data from visual estimates, which is unprecedented in its sensitivity to spatial trends in bird damage. I also review its valid use in comparative statistical analysis. Spatial trends in 3 out of 4 study plots confirmed a priori predictions about localisation in bird damage based on optimal foraging from a central location (staging area). Damage to grape clusters was: (1) greater near the edges of vineyard plots and decreased with distance towards the center, (2) greater in areas adjacent to staging areas for birds, and (3) vertically stratified, with upper-tier clusters sustaining more damage than lower-tier clusters. From a management perspective, this predictive approach provides vineyard owners with the ability to identify the portions of plots likely to be most susceptible to bird damage, and thus the opportunity to focus deterrent measures in these areas. Other management considerations at Henry of Pelham were: (1) wind damage to ice-wine Riesling and Vidal was much higher than bird damage, (2) plastic netting with narrow mesh provided more effective protection agsiinst birds than nylon netting with wider mesh, and (3) no trends in relative susceptibility of varietals by colour (red vs green) were evident.

Postglacial paleoecology and effects of European settlement on the environment of Lake Hunger and Lake Lisgar, Southwestern Ontario /

This investigation has three purposes I to make a comparative chemical study on sediment cores collected for Lake Lisgar (man-made lake in an urban center) and Lake Hunger (natural basin in a rural community) encompassing the time since European settlement I to determine the postglacial chemical history of Lake Hunger, and to determine the vegetational history of the Lake Hunger area from postglacial time to the present. The minus 80 mesh fraction of 108 soil samples and 18 stream sediment samples collected in the vicinity of Lakes' Lisgar and Hunger were analyzed for cold hydrochloric acid soluble lead, zinc, nickel, cobalt, copper, aluminum, sodium, potassium, calcium, magnesium, iron and manganese. Lacustrine sediments from 5 boreholes in the Lake Lisgar basin were collected. Boreholes 1, 2, 3, and 4 were analyzed for palynological and chemical information and Borehole 5 was subjected to pollen and ostracode analysis. Lacustrine sediments from 6 boreholes in the Lake Hunger basin were collected. Palyno- -logical and chemical analysis were performed on Boreholes 1, 2, 3, 4, and 6 and Borehole 5 was analyzed for pollen. In addition, radiocarbon dates were obtained on sediment samples from Boreholes 4 and 5. A total of 8 surface samples were collected from the margins of the Lake Hunger basin and these were chemically analyzed in the laboratory. All of the lacustrine sediments were ashed and analyzed for cold hydrochloric acid soluble lead, zinc, nickel, cobalt, copper, aluminum, sodium, potassium, calcium, magnesium, iron and manganese using a Perkin Elmer 40) Atomic Absorption spectrophotometer. The results . obtained for the 12 elements were expressed as parts per million in dry sediments. It was found that man's influence on the element distribution patterns in the sediments of Lake Lisgar appeared to be related to his urbanizing developments within the lake vicinity, whereas, the rural developments in the vicinity of lake Hunger appeared to have had little effect on the element distribution patterns in the lake sediments. The distribution patterns of lead, zinc, nickel, cobalt, aluminum, magnesium, sodium and potassium are similar to the % ash curve throughout postglacial time indicating that the rate of erosion in the drainage basin is the main factor which controls the concentration of these elements in the sediments of Lake Hunger. The vegetational history, from palynological analysis, of Lake Hunger from postglacial time to the present includes the following stages: tundra, open spruce forest, closed boreal forest, deciduous forest and the trend towards the re-establishment of pine following the clearing of land and the subsequent settlement of the Lake Hunger area by European settlers. The concentrations of some elements (cobalt, nickel, iron, manganese, calcium, magnesium, sodium and potassium) in the sediments of Lake Hunger appears to be higher during pre-cultural compared to post-cultural times. At least one complete postglacial record of the chemical history within a lake basin is necessary in order to accurately assess man's effects on his environment.

Impact of considering the effects of latent heat on caldera-hosted hydrothermal systems

To investigate the thennal effects of latent heat in hydrothennal settings, an extension was made to the existing finite-element numerical modelling software, Aquarius. The latent heat algorithm was validated using a series of column models, which analysed the effects of penneability (flow rate), thennal gradient, and position along the two-phase curve (pressure). Increasing the flow rate and pressure increases displacement of the liquid-steam boundary from an initial position detennined without accounting for latent heat while increasing the thennal gradient decreases that displacement. Application to a regional scale model of a caldera-hosted hydrothennal system based on a representative suite of calderas (e.g., Yellowstone, Creede, Valles Grande) led to oscillations in the model solution. Oscillations can be reduced or eliminated by mesh refinement, which requires greater computation effort. Results indicate that latent heat should be accounted for to accurately model phase change conditions in hydrothennal settings.

Mechanisms of long-term modulation of synaptic transmission in crayfish

Please consult the paper edition of this thesis to read. It is available on the 5th Floor of the Library at Call Number: Z 9999 B56 M68 2007

Action of octopamine and tyramine on muscles of Drosophila melanogaster larvae

Octopamine (OA) and tyramine (TA) play important roles in homeostatic mechanisms, behavior, and modulation of neuromuscular junctions in arthropods. However, direct actions of these amines on muscle force production that are distinct from effects at the neuromuscular synapse have not been well studied. We utilize the technical benefits of the Drosophila larval preparation to distinguish the effects of OA and TA on the neuromuscular synapse from their effects on contractility of muscle cells. In contrast to the slight and often insignificant effects of TA, the action of OA was profound across all metrics assessed. We demonstrate that exogenous OA application decreases the input resistance of larval muscle fibers, increases the amplitude of excitatory junction potentials (EJPs), augments contraction force and duration, and at higher concentrations (10−5 and 10−4 M) affects muscle cells 12 and 13 more than muscle cells 6 and 7. Similarly, OA increases the force of synaptically driven contractions in a cell-specific manner. Moreover, such augmentation of contractile force persisted during direct muscle depolarization concurrent with synaptic block. OA elicited an even more profound effect on basal tonus. Application of 10−5 M OA increased synaptically driven contractions by ∼1.1 mN but gave rise to a 28-mN increase in basal tonus in the absence of synaptic activation. Augmentation of basal tonus exceeded any physiological stimulation paradigm and can potentially be explained by changes in intramuscular protein mechanics. Thus we provide evidence for independent but complementary effects of OA on chemical synapses and muscle contractility.

The role of retinoic acid in long-term memory formation and synaptic plasticity in the mollusc Lymnaea stagnalis

The active metabolite of vitamin A, retinoic acid (RA), is involved in memory formation and hippocampal plasticity in vertebrates. A similar role for retinoid signaling in learning and memory formation has not previously been examined in an invertebrate species. However, the conservation of retinoid signaling between vertebrates and invertebrates is supported by the presence of retinoid signaling machinery in invertebrates. For example, in the mollusc Lymnaea stagnalis the metabolic enzymes and retinoid receptors have been cloned from the CNS. In this study I demonstrated that impairing retinoid signaling in Lymnaea by either inhibiting RALDH activity or using retinoid receptor antagonists, prevented the formation of long-term memory (LTM). However, learning and intermediate-term memory were not affected. An additional finding was that exposure to constant darkness (due to the light-sensitive nature of RA) itself enhanced memory formation. This memory-promoting effect of darkness was sufficient to overcome the inhibitory effects of RALDH inhibition, but not that of a retinoid receptor antagonist, suggesting that environmental light conditions may influence retinoid signaling. Since RA also influences synaptic plasticity underlying hippocampal-dependent memory formation, I also examined whether RA would act in a trophic manner to influence synapse formation and/or synaptic transmission between invertebrate neurons. However, I found no evidence to support an effect of RA on post-tetanic potentiation of a chemical synapse. Retinoic acid did, however, reduce transmission at electrical synapses in a cell-specific manner. Overall, these studies provide the first evidence for a role of RA in the formation of implicit long-term memories in an invertebrate species and suggest that the role of retinoid signaling in memory formation has an ancient origin.

The action of octopamine on muscles of Drosophila melanogaster larvae

Octopamine (OA) and tyramine (TA) play important roles in homeostatic mechanisms, behavior, and modulation of neuromuscular junctions in arthropods. However, direct actions of these amines on muscle force production that are distinct from effects at the neuromuscular synapse have not been well studied. We utilize the technical benefits of the Drosophila larval preparation to distinguish the effects of OA and TA on the neuromuscular synapse from their effects on contractility of muscle cells. In contrast to the slight and often insignificant effects of TA, the action of OA was profound across all metrics assessed. We demonstrate that exogenous OA application decreases the input resistance of larval muscle fibers, increases the amplitude of excitatory junction potentials (EJPs), augments contraction force and duration, and at higher concentrations (10(-5) and 10(-4) M) affects muscle cells 12 and 13 more than muscle cells 6 and 7. Similarly, OA increases the force of synaptically driven contractions in a cell-specific manner. Moreover, such augmentation of contractile force persisted during direct muscle depolarization concurrent with synaptic block. OA elicited an even more profound effect on basal tonus. Application of 10(-5) M OA increased synaptically driven contractions by ≈ 1.1 mN but gave rise to a 28-mN increase in basal tonus in the absence of synaptic activation. Augmentation of basal tonus exceeded any physiological stimulation paradigm and can potentially be explained by changes in intramuscular protein mechanics. Thus we provide evidence for independent but complementary effects of OA on chemical synapses and muscle contractility.

Cell-selective modulation of the neuromuscular system in Drosophila

The capacity for all living cells to sense and interact with their environment is a necessity for life. In highly evolved, eukaryotic species, like humans, signalling mechanisms are necessary to regulate the function and survival of all cells in the organism. Synchronizing systemic signalling systems at the cellular, organ and whole-organism level is a formidable task, and for most species requires a large number of signalling molecules and their receptors. One of the major types of signalling molecules used throughout the animal kingdom are modulatory substances (e.x. hormones and peptides). Modulators can act as chemical transmitters, facilitating communication at chemical synapses. There are hundreds of circulating modulators within the mammalian system, but the reason for so many remains a mystery. Recent work with the fruit fly, Drosophila melanogaster demonstrated the capacity for peptides to modulate synaptic transmission in a neuron-specific manner, suggesting that peptides are not simply redundant, but rather may have highly specific roles. Thus, the diversity of peptides may reflect cell-specific functions. The main objective of my doctoral thesis was to examine the extent to which neuromodulator substances and their receptors modulate synaptic transmission at a cell-specific level using D. melanogaster. Using three different modulatory substances, i) octopamine - a biogenic amine released from motor neuron terminals, ii) DPKQDFMRFa - a neuropeptide secreted into circulation, and iii) Proctolin - a pentapeptide released both from motor neuron terminals and into circulation, I was able to investigate not only the capacity of these various substances to work in a cell-selective manner, but also examine the different mechanisms of action and how modulatory substances work in concert to execute systemic functionality . The results support the idea that modulatory substances act in a circuit-selective manner in the central nervous system and in the periphery in order to coordinate and synchronize physiologically and behaviourally relevant outputs. The findings contribute as to why the nervous system encodes so many modulatory substances.